At valor rank 40 you can begin banking commendations of the regular variety as ranked commendations through PVP vendors, and if you're leveling purely through PVP this will allow you to bank a significant chunk of ranked commendations before hitting 50. Math escapes me but it should be possible to get a piece of war hero as soon as you hit 50 with capped comms and a nice reserve of ranked comms.
Yeah, you can hold 3500 ranked warzone commendations and 2000 warzone commendations, meaning that if you hit lvl 50 with those numbers you can instantly buy either a few pieces of battlemaster clothing and a few war hero bonuses (implants, earpieces or relics), or buy, for example, a battlemaster main hand weapon and immediately upgrade it to war hero.
//Also, this came to me immediately after I converted my mercenary commendations to warzone commendations after 1.2, but IF THERE IS STILL SOMEONE UNDER 50 AROUND THERE WITH WARZONE COMMENDATIONS, don't use them. You get a free max-1000 commendations to hold, just exchange them to warzone commendations when the time of need comes.